"We are so blessed to be engaged! God has written an amazing story through our courtship, and another chapter has just begun!" the giddy couple said in a statement. "We are thrilled to see what the future holds – especially the wedding bells!"

Duggar, 21, is third daughter of Jim Bob, 48, and Michelle, 47. Their show starts its new season Sept. 2 (9 p.m. ET).

"We do have a lot in common," she told PEOPLE during her courtship with Seewald, 19. "He is a mellow personality, very romantic and very sweet. I am very cut and dried. And my sisters are coaching me on sweet romantic things to say."

"People always ask us when we are getting married," Seewald told PEOPLE at the wedding of his soon-to-be sister- and brother-in-law. "We don't feel pressure to get married. If there's any pressure, it's a good kind of pressure."

Now that they're planning a wedding of their own, how will the newest member of the Duggar family handle the spotlight of reality television?

"The Duggar family gets asked a lot of questions," he told PEOPLE. "A lot of times we take it as a lesson, and we ask other people who are older and wiser than us to share wisdom with us about relationships. It's an important thing."

Like Duggar's parents, she and her new fiancé say they want to have a big family, and leave the number of children they have "up to God." Seewald is the oldest of seven children.

"We are talking about our goals and even just like future, with family, we both talked about adoptions," Duggar told PEOPLE. "We are open to having children and both want to adopt, too."